1. Field of the Invention
The present invention relates to a nuclear magnetic resonance spectrometer using a sample tube for a sample whose shape is deformable, and a method for operation thereof.
2. Description of the Related Art
The shapes of a sample tube and a detection coil in a nuclear magnetic resonance spectrometer (which will be referred to as a NMR system hereinafter) as shown in FIG. 2 are well-known. For example, a sample tube shown in FIG. 2 in JP-A-06-249934 has a shape similar to that of a common test tube, and in measuring thereof, the sample tube is inserted into a central portion of a NMR magnet adapted to generate an intense static magnetic field.
A housing 12 of a detecting device (probe) and a measuring coil 14 are disposed around the inserted sample tube 10 to surround the sample tube 10. A gas 15 is also present between the sample tube 10 and the housing 12 of the detecting device. In general, a sample solution 18, the sample tube 10 and the gas 16 are different in magnetic permeability from one another, and hence, a boundary surface perpendicular to the static magnetic field is magnetized to disturb the static magnetic field around the boundary surface.
For example, when the static magnetic field generated by the magnet faces in an axial direction of the sample tube 3, the static magnetic field is disturbed at vertically opposite ends of the sample solution 18 and the sample solution 20, i.e., at portions outside the boundary. In order to reduce the adverse affection exerted to an NMR spectrum by the disturbance of the static magnetic field, only a signal transmitted from a sample portion 18 of the sample solutions 18 and 20 filling the sample tube 10, which is present at a central portion where the static magnetic field is not disturbed, is detected by the measuring coil 14. The signal emitted from that portion of the sample solution 20 exists outside a space surrounded by the coil 14 and cannot reach the measuring coil 14, because of a low sensitiveness of the measuring coil 14.
In the system shown in FIG. 2 and described in JP-A-06-249934, the uniformity of the static magnetic field is poor, and in order to prevent the degradation of the NMR spectrum due to the disturbance of the static magnetic field, a surplus sample 20 to be measured is required in addition to the sample solution 18 to be measured, which makes it difficult to analyze a very small amount of a sample. In order to improve the problem associated with JP-A-06-249934, JP-A-05-249214 has been proposed. A system described in this JP-A-05-249214 includes a spherical (in general, elliptic) measuring space into which a sample solution 18 to be measured is placed, and a capillary tube 22 for introduction of a sample solution into the measuring space, as shown in FIG. 3.
According to JP-A-05-249214, the shape of the sample solution is spherical or elliptic, and in the static magnetic field which is uniform spatially, the static magnetic field in the sample solution can be uniformized irrespective of the sample solution 18 and the magnetic permeability of the sample tube 10 and the peripheral gas 16. This is because a difference in permeability between inside and outside the ellipse disturbs the magnetic field around the sample solution 18, but does not disturb the internal magnetic field in the sample solution 18, according to an electro-magnetological law. Therefore, in the system described in JP-A-05-249214, the uniformity of the static magnetic field can be enhanced by forming the sample solution into the elliptic shape. However, as can be seen from the geometrical dispositions of the sample tube 10 and the measuring coil 14 as shown in FIG. 3, the distance between the measuring coil 14 and the sample solution 18 is larger, and the measuring sensitivity is lower.